Periodic wave-generating system



Dec. 19, 1939.

H. M. I Ewls PERIODIC WAVE-GENERATING SYSTEM Filed Dec. 22, 1937 2Sheets-Sheet 1 ATTORNEY Dec. 19, 1939. H. M. LEwls PERIODICWAVE-GENERATING SYSTEM Filed Dec. 22, 1937 2 Sheets-Sheet 2...ll-1li...4 u

INVENTOR H ROLD M. LEWI @ma Vo .3a. o 1o.... i L f n f f r n u r r n r fr f f f n f f r o mda Mu) o .N61

ATTORNEY Patented Dec. 19, 1939 UNITED STATES PATENT OFFICE Harold M.Lewis, Great Neck, N. Y., assigner to Hazeltine Corporation, acorporation of DelawareA Application December 22, 1937, Serial No.181,129

9 Claims.

This invention relates to periodic wave-generating systems. Theinvention is especially concerned with the provision of awave-generating system for developing a scanning-synchronizing signalfor use in a television system.

In accordance with present television practice, there is developed andtransmitted a signal which comprises a carrier wave, modulated duringrecurring intervals or trace periods by video-frequency componentsrepresentative of light and shade values of an image being transmitted.During the retrace intervals, between the trace periods, the carrierwave is modulated by a composite synchronizing signal which comprisesim- 1" pulses or components corresponding to the initiations ofsuccessive lines and elds in the scanning of the image. At the receivera beam is so deflected as to scan and illuminate a target in a series ofsuccessive elds of parallel lines, the video-frequency components of thesignal being utilized to control the intensity of the beam. Theline-synchronizing and field-synchronizing components are separated fromthe video-frequency components and from each other and utilized to 25synchronize the operation of the receiver linescanning andfield-scanning apparatus with the corresponding apparatus utilized atthe transmitter in developing the signal. The transmitted image isthereby reproduced on the target of the receiver.

In scanning of the interlaced type, line and field frequencies are sorelated that successive fields are staggered, the lines of one fleldfalling between or interlacing those of a preceding field 35 and, due topersistence of Vision, an optical effect is produced as though eachfield comprised a multiple of the actual number of lines scanned pereld.

Various types of synchronizing signals and ap- 40 paratus for developingthem have heretofore been proposed, the type of signal requiredordinarily being dependent upon the type of scanning utilized. Whereinterlaced scanning is employed, certain of the field-synchronizingimpulses must 45 occur between line-synchronizing impulses and,

in order that the line-synchronizing and framesynchronizing impulses ofthe composite synchronizing signal may be successfully separated fromeach other and utilized, a special type of 5o synchronizing signal isrequired. One such type of signal which has been proposed comprisesline-synchronizing and frame-synchronizing impulses of the sameamplitude, but with the latter of substantially longer duration than theformer 55 and serratedto permit uninterrupted recurrence (Cl. Z50-$6) ofthe former. Such a signal may be developed by generating aline-synchronizing impulse wave of the desired frequency and, inaddition, generating a similar alternate-impulse wave and aparabolic-impulse wave, the alternate wave being 5 of the line-scanningfrequency but having its impulses so displaced in phase as to occurbetween the line-synchronizing impulses, and the parabolic wave being ofdouble the line-scanning frequency with its impulses in such phase as tooccur intermediate the line-synchronizing and alternate impulses. Thesethree waves may then be periodically combined at field-scanningfrequency intervals and for predetermined durations, thereby to producethe desired serrated fleld-synchronizing impulses, Certain difculties,however, are presented in the development of the several waves in theprecise synchronism required to procure the necessary phaserelationships, this being particularly true with regard to thelinesynchronizing and alternate-impulse waves.

It is an object of the present invention, therefore, to provide animproved periodic composite impulse wave-generating system.

More particularly, it is an object of the invention to provide a systemof the character described whichis especially adapted in developing acomposite synchronizing signal for use in a television system.

In accordance with the present invention there is provided a. periodicwave-generating system which comprises means for generating a firstperiodic-impulse wave of a predetermined fresecond waves. This latermeans may comprise 5 a direct connection between the two generatingmeans for controlling the operation of one in accordance with theoperation of the other.

Each of the generating means may comprise energy-storage means withcharging and discharging circuits therefor and suitable control means,such as a vacuum tube, for controlling these circuits to eiect periodiccharging and discharging of the storage means. The control conmotionbetween the two generating means preferably serves to disable onecircuit of one of thc generating means during operation of thecorresponding circuit of the other of the generating means. Anarrangement for generating wave forms of the general type of thoseutilized in the present invention and which, per se, forms no part ofthe present invention is disclosed and broadly claimed in a copendingapplication of Madison Cawein, Serial No. 176,963, filed November 29,1937, and assigned to the same assignee as the present application. o

For -a better understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawings, and itsscope willbe-pointed out in the appended claims.

In the accompanying drawings, Fig. 1 is a circuit diagram, partiallyschematic, of a complete television transmitting apparatus embodying theinvention; while Figs. 2-7, inclusive, are curves illustrating the waveforms of periodic waves developed at various points of the system ofFig. 1 to aid in the understanding of the invention.

Referring now more particularly to Fig. llof the drawings,` there isillustrated a television transmitting system comprising a cathode-raysignal generator I0, which may be of a conventional design and includethe usual 'signal-generating tube, camera, and scanning elements.v

For the purpose of developing scanning voltages or currents for thegenerator I0, there are provided .a line-frequency saw-tooth wavegenerator II and a field-frequency saw-tooth wave generator I2, theoutput circuits of these generators being connected to the scanningelements of the.

signal generator ID in the usual manner. In order to blocli out thecathode ray of the generator I0 during the retrace scanning periods,there is provided a block-out wave generator I3 having its outputcircuit suitably connected to the signal generator I0. For providingpedestal impulses to suppress undesirable signal impulses during retracescanning periods and to ensure the proper form of the modulation signalto be developed, there is provided a pedestal-impulse generator I4 and,in order to develop a composite scanning-synchronizing signal inaccordance with the present invention, there is provided a synchronizingsignal generator I5. The generator I5 comprises a line-synchronizingimpulse-wave generator I6, an alternate-impulse wave generator I1, aparabolic-impulse wave generator I8, and a signal-combining network I 9.Suitable control circuits 20 and 2| are provided in connection with thecombining network.4 For the purpose of synchronizing the generators II-I4, inclusive and lli-I8, inclusive, and the control circuits 20 and2|, there is provided for the system a timing-impulse generator 22 towhich are coupled the input circuits of the last-mentioned generatorsand control circuits. Preferably, the generators I6I8, inclusive, areall connected to a, single output circuit of the generator 22, acrosswhich is developed a periodic synchronizing-impulse wave of double thedesired line-scanning frequency, for example, 26,460 cycles for 441 lineinterlaced scanning with a field frequency of 60 cycles.

In accordance with the present invention as hereinafter described, thegenerators I6 and I1 are arranged to be individually synchronized bysuccessive impulses of the double-frequency wave, while theparabolic-impulse wave generator I8 develops -a wave of the doublefrequency and is synchronized by all of the impulses of the timing wavefrom generator 22. The generator 22 is preferably stabilized by means ofa connection 23 to a suitable source of periodic voltage, for example,the power supply circuit or the synchronizing source of motion picturemechanism,where such is employed.

Connected in cascade to the output circuit of the cathode-ray signalgenerator I0, in the order named, are video-frequency ampliers 24, 25,and 26, a modulator 2l and'asso'ciated coupled oscillator 28, a poweramplifier 29, and an antenna system 30, 3 I, all according toconventional practice. The output circuit of the pedestal generator I4is coupled to the video-frequency amplifier 25, while the output circuitof the combining network I9 is coupled to the video-frequency amplifier26.

Neglecting for the moment the details of the synchronizingsignal-generating apparatus which embodies the present invention, thesystem just described comprises a television transmitting system ofconventional design and the various parts thereof, illustratedschematically, being of wellknown construction, a detailed descriptionof the o general system and its operation is unnecessary.

Briefly, however, the image of a scene to be transmitted is focused onthe target of the cathoderay tube of the signal generator Ill, in whichtube a cathode ray is developed, focused, and accelerated toward thetarget in the usual manner. Scanning or deflecting currents or voltagesdeveloped by the generators II and I2 are applied to the scanningelements of the generator I0 to provide electric fields which serve todeflect the cathode ray horizontally and vertically, thereby to scansuccessive series of parallel lines or fields upon the target. Thedeecting currents or voltages and, hence, the scanning elds are ofwellknown saw-tooth form providing a relatively slow linear trace andrapid retrace. The number of lines per field are determined by therelative fieldscanning and line-scanning frequencies and thesefrequencies are preferably such, for example, 26,460 kilocycles and 60cycles, respectively, that the successive fields are staggered orinterlaced in the well-known manner. Block-out impulses developed by thegenerator I3 are applied to a control electrode of the cathode-ray tubeto suppress or block-out the beam during retrace portions of thescanning cycles, while pedestal impulses developed by the generator I4are applied to the amplifier 25 to suppress surges developed during theretrace period and to modify the resultant video-frequency wavedeveloped, thereby to aid in the separation of line-synchronizing andframe-synchronizing impulses at the receiver.

The synchronizing impulses developed by the generators I6-I8, inclusive,are combined inA thc network I9 and applied therefrom as a compositesynchronizing signal to the modulation amplifier 26. 'Timing impulsesdeveloped by the generator 22 are applied to the generators I I-I4,inclusive, and Iii-I8, inclusive, and to the control circuits 20, 2| tolock these generators in synchronism.

4The photosensitive elements of the target in the cathode-ray tubegenerator 'I0 being electrically affected to an extent depending uponthe varying values oi. light and shade at incremental areas of theimages focused thereon as the cathode-ray scans the target, avideofrequency voltage 4of correspondingly varying amplitude isdeveloped in the output circuit of the generator I 0 and applied to thevideo-frequency amplifier 24, wherein this voltage is amplied and fromwhich it is translated to the amplifier 25. Here the video-frequency.voltages are .further amplified and mixed with the pedestal impulsessupplied from the generator I4. The mixed amplified voltages in theoutput circuit of the amplifier are thereupon applied to the amplifier26, wherein they are further amplified and mixed with the compositesynchronizing signal supplied from the combining network I9. Thecomposite modulation signal is then supplied to the modulator 21,wherein it is impressed upon the carrier wave generated by theoscillator 28, and the resultant modulated-carrier signal is deliveredto the power amplifier 29 for amplification and is thereafter impressedupon the antenna system 30, 3I to be broadcast.

Referring now more particularly to the apparatus embodying the presentinvention and the circuits associated therewith, the compositesynchronizing signal-generating apparatus I5 includes, as stated above,the line-synchronizing impulse wave generator I6, the alternate-impulseY wave generator I1, and the parabolic-impulse wave generator I8. Thegenerator I6 includes energy-storage means, such as axcondenser 32,having a resistor 33 in series therewith, the latter having an impedancewhich is relatively very small compared to that of the condenser 32 atthe oscillation frequency. A charging circuit is provided for thecondenser 32 which includes a source of direct current, for example, abattery 34, preferably grounded at its negative terminal, a resistor 35and thespace current path of a vacuum tube 36. A discharging circuitcomprising an adjustable resistor 31 is connected across the condenser32. The tube 36 serves as means for controlling the charging anddischarging circuits to effect periodic charging and discharging of thecondenser 32. There is also provided regenerating tube 38 having itscathode grounded and its anode connected to the control electrode of thetube 36, while the control grid of the regenerating tube is connected byway of a suitable coupling condenser 39 to the anode of the tube 36.- Abuffer amplifier tube 40 is preferably interposed between the generator,per se, and the timing-impulse generator 22 to which it is coupled byway of a suitable condenser 4I to receive synchronizing or controlimpulses of twice the line-scanning frequency. A suitable grid-leakresistor 42 is connected between the control grid and cathode of thetube 40, while operatingI potentials vmay be supplied to the anodes ofthe tubes 38 and 49 from a battery 43 by way of a common load resistor44. A leak resistor 45 is connected to the grid of the regenerating tube38 and is utilized in accordance with the'present invention, as will bepresently explained. The alternate-impulse wave generator I'I is of thesame construction and operation as the generator I6, similar elementsbeing designated by the same reference numerals with theV suffix a.

For the purpose of controlling the operation of each of the generatorsI6, I1 in accordance with the operation of the other, or moreparticularly to disable one of the charging or discharging circuits ofone of these generators during the operation of the correspondingcircuit of the other generator, there is provided a direct connection46, including resistor 45a, between the control grid of the regeneratingtube 38a of the generator I1 and the high potential terminal of theresistor 33 of the generator I6. If desired, a similar additionalconnection 41, including resistor 45, may be provided between thecontrol grid of the regenerating tube 38 of generator I8 and the highpotential terminal of-the resistor 33a of generator I1.

The combining network I9 preferably comprises three high impedancepentode amplifier tubes 48, 49, and 50. The output circuits, includingthe leads 46a and 41a, of the generators I6 and I1 are connected to thecontrol grids of the tubes 50 and 49, respectively, while the outputcircuit of the parabolic-impulse generator I8 is connected to thecontrol grid of the tube 48,. The

anode circuits of these tubes are connected in l paralleland coupled tothe amplifier 26 by way of a coupling condenser 6I Operating potentialsare supplied to the anodes of the tubes by way of load resistor 52 andchoke 53 and to the screens from suitable sources indicated generally at+B and-i-Sc. 'I'he suppressor grids of the tubes 48 and 49 are normallybiased sufficiently negatively to maintain these tubes nonconductive, asby means of batteries 54 and leak resistors 55. The suppressor grids ofthe tubes 48 and 49, however, are also coupled to the control circuits20 and 2 I, respectively, each of which comprises suitable LettersPatent No. 2,052,184, granted August 25,.

1936, upon the application of Harold M. Lewis, generatingperiodic-impulse waves of line-scanning frequency in a manner wellunderstood in the art, so that a detailed explanation thereof isunnecessary. Briey, however, in generator I6, the condenesr 32 israpidly charged from the source 34 by way of the tube 36 and isdischarged at a relatively slow rate through the resistor 31. Thedischarging action continues until the potential diference developedacross the tube 36 is sufdcient, upon the application of a synchronizingimpulse to its control grid from the generator 22, to break down thetube 36 and initiate another charging action. The initial surge ofcharging current results in a voltage impulse across the resistor 35which is impressed negatively by way of condenser 39 upon the controlgrid offthe regenerating tube 38, reducing its conductivity. A positiveimpulse peak is thereby developed across the load resistor 44 andapplied to the control grid of the tube 36 to accelerate or regenerateits charging action. The synchronizing or timing impulses from thegenerator 22 are applied to the control grid of the tube 36 by way ofthe condenser 4I and the buffer amplifier 40 and serve to synchronizethe operation of the generator at the line-scanning frequency.

The periodic charging and discharging ofv the condenser 32 causes avoltage to be developed thereacross which has a saw-tooth wave form and,hence, a current flows through the condenser 32 and resistor 33 whichhas a periodic rectangular-impulse wave form, that is, a wave form whichis the rst derivative' of the sawtooth voltage wave form. 'Ihis voltageis impressed upon tube 50 of the combining network auV I 8 by way of theleads 46 and 46a. Similarly, the generator II developsva voltage acrossthe resistor 33a which is applied by way of the leads 4l and 41a to tube48 of the combining network. The natural frequencies of the generatorsI3 and l1, that is, the frequency at which they would operate withoutsynchronizing control, are slightly lower than the desiredline-synchronizing frequency to ensure operation at half the appliedsynchronizing frequency, the latter being double the line frequency.

Assuming a point in the cycle when the tube 36 is passing current tocharge its condenser 32, the current is then flowing through theresistor 35 in its anode circuit biasing the control grid of thereversing tube 38 negatively, which is the proper direction to effectthe regenerative action, while the current is flowing through resistor33 in series with the condenser 32 in such direction as to developthereacross a positive voltage which is applied to the control grid ofthe reversing tube 38a. This positive voltage is in the proper sense tocause the reversing tube 38a to block the tube 36a, that is, it isopposite to that required for regeneration of generator II so that theinitiation of the next cycle of this generator is prevented. Similarly,the voltage developed across the resistor 33a during charging ofcondenser 32a of the generator Il is applied to the control grid of theregenerating tube 38 of the generator I6 to prevent the initiation ofthe next cycle of this generator during charging of generator I'I. Thatis, the charging circuit of each generator is disabled during thecharging operation of the other generator. Obviously, therefore, the twogenerators, while having a synchronizing-impulse wave from generator 22applied thereto which is of double the frequencies developed thereby,are selectively synchronized by successive impulses of this wave. Inother words, the predetermined phase displacement between the impulsesof the waves developed by the two generators is maintained.

The general operation oi' the system may be explained with reference tothe curves oi.' Figs. 2-7, inclusive, which show the wave forms of thevoltages or currents developed at various points in the system. Fig. 2represents the signal appearing at the output circuit of thevideo-frequency amplier 25, video-frequency impulses indicated at Vhaving been supplied from the cathode-ray signal generator I0 andline-frequency and frame-frequency pedestals p1 and pr having beendetermined or formed by voltage from generator I4 mixed with thevideo-frequency signal in the amplifier 25. The curve of Fig. 3represents the double line-frequency synchronizingimpulse wave developedin one of the output circuits of the timing generator 22 and applied tothe input circuits of the generators I6, Il, and I8. The curve of Fig. 4represents the line-synchronizing impulse wave developed by thegenerator I6 and applied to the input circuit of the tube 58, while thecurves of Figs. 5 and 6 represent the alternate line-frequency impulsewave and parabolic-impulse wave, the latter being at the double-linefrequency developed by the generators Il and I8 and applied to the inputcircuits of the tubes 49 and 48, respectively. As explained above,alternate-line impulses occur intermediate the line-scanning impulses,while the parabolic impulses occur between the succeeding impulses' ofthe combined line-synchronizing impulse and alternate-impulse waves.

The final desired modulation signal developed by the system is of thewave form shown in Fig. 7, including the video-frequency voltages aswell as the composite synchronizing signal. To develop such a wave, theline-synchronizing impulses are repeated continuously by the tube 6l.its operating voltages being such as to eifect this operation, while thealternate impulses are added during a part of the retrace portion ofeach fieldfrequency cycle, this portion corresponding to the duration ofthe field-frequency pedestal. During a part ofthe line-doubling period,the parabolic impulses are added or inserted 'between theline-synchronizing and alternate impulses to provide, in efi'ect,relatively long serrated ileld-synchronizing impulses for each ieldcycle without interruption of the line-synchronizing impulses. Thecombined synchronizing signal is then combined with the video signal, asstated above, in the amplier 28.

The line-doubling and inserting operations are effected at the propertimes and for the proper durations by virtue of the actions of tubes 48and 49, controlled by their respective control circuits 20 and 2|. Moreparticularly, since these two tubes are normally biased beyond cutoff bythe suppressor bias batteries 64, they are normally nonconductive andthe alternate and parabolic Waves do not appear in the common outputcircuit of the network I9. The positive control impulses which aresupplied by the circuits 20 and 2 I, however, serve to unblock thesetubes for predetermined periods at the field-scanning frequency, therebyto eil'ect the combining actions, as described above.

In Figs. 2 and 7 the points :n and z' correspond to the beginning andtermination, respectively, of the frame-pedestal impulses, such as aresupplied by the generator I4. 'I he line doubling, or addition ofalternate impulses, takes place during the time interval between thepoints indicated at y and y in Fig. 7, the initiation of this actionbeing preferably delayed for the period represented at d1. The addition0r insertion of the parabolic impulses takes place between the points zand z', the initiation of this action being delayed for a periodrepresented as dz. The control circuits 20 and 2l include suitableapparatus for effecting the required delays and durations of the controlimpulses.

The output circuits of the tubes", 4 9, and 80 being connected inparallel, when these tubes are conductive the signals impressed on theirinput circuits are combined in their common output circuit, the tube 50continuously repeating the line-synchronizing impulses (Fig. 4) receivedfrom the generator I6 and the tubes 4l and 48 operating intermittently,as described above. The combined synchronizing signal is thus developedin the output circuit of the combining network I9, supplied to theampliner 26, and therein mixed with the video-frequency signal, theresultant modulation signal of the desired wave form shown in Fig. 7being thus obtained.

While therehas beendescribed what is at present considered to be thepreferred embodi- -ment of this invention, it will be obviousto thoseing a generator for generating a rst periodic wave of a predeterminedfrequency, a separate generator for independently generating a secondperiodic wave of said predetermined frequency, a synchronizing circuitadapted for the reception of a synchronizing wave of double saidpredetermined frequency and coupled directly to each of said generatorsfor synchronizing their respective operations, and means for ensuringselective synchronization of said two generators by successive cycles ofsaid synchronizing wave comprising a direct connection between saidgenerators for controlling the operation of one in accordance with theoperation of the other.

2. 'A periodic wave-generating system, comprising a generator forgenerating a first periodic Wave of a predetermined frequency, aseparate generator for independently generating a second periodic waveof said predetermined frequency, each of said generators comprisingenergy-storage means, charging and discharging circuits for said storagemeans, and a control circuit for controlling said charging anddischarging lcircuits to effect periodic charging and discharging orsaid storage means, and means for coupling the control circuit of one ofsaid generators to one of the charging and discharging circuits of theother of said generators for disabling the corresponding circuit of saidone of said generators during operation of said corresponding circuit ofthe other of said generators.

3. A periodic wave-generating system, comprising means for generating arst periodic Wave of a predetermined frequency, means for generating asecond periodic wave of said predetermined frequency, each of saidgenerating means comprising energy-storage means, chargand dischargingcircuits for said storage means and means for controlling said circuitsto eiect periodic charging and discharging of said storage means, andmeans coupling said generating means to prevent charging of the storagemeans of one of said generating means during charging of the storagemeans of the other of said generating means.

4. A periodic wave-generating system, comprising means for generating arst periodic wave of \a\ predetermined frequency, means for generating asecond periodic wave of said predetermined frequency, a synchronizingcircuit adapted for the reception of a synchronizing wave of double saidpredetermined frequency and coupled to said generating means forsynchronizing their respective operations, each of said generating meanscomprising energy-storage means, charging and discharging circuits forsaid storage means, and means for controlling said circuits to eiect aperiodic charge and discharge of said capacitance means, and means forensuring selective synchronization of said two generating means bysuccessive cycles of said synchronizing Wave comprising means couplingsaid generating means to prevent charging of the storage means of one ofsaid generating means during charging of the storage means of the otherof said generating means.

5. A periodic wave-generating system, comprising means for generating afirst periodic wave of a predetermined frequency, means for generating asecond periodic wave of said predetermined frequency, each of saidgenerating means comprising energy-storage means, charging anddischarging circuits for said storage means, means for controlling saidcircuits to effect a periodic charge and discharge of said storage meansand means for regenerating the action of said control means, and meanscoupling the charging circuit of one of said generating means to theregenerating means of the other of said generating means to preventcharging of the storage 4means of said other generating means duringcharging of the storage means of said one of said generating means.

6. A periodic voltage-generating system, comprising means for generatinga rst periodic wave of a predeterminedA frequency, means for generatinga second periodic wave of said predetermined frequency, each of saidgenerating means comprising energy-storage means, charging anddischarging circuits for said storage means, and a vacuum tube includedin said charging circuit for effecting periodic charging and dischargingcf said storage means, an impedance element in series with said tube inthe charging circuit of one of said generating means, and meansconnecting a control element of the other of said generating meansacross said impedance element for preventing charging of the storagemeans of said other generating means during charging of the storagemeans of said one generating means.

7. A periodic voltage-generating system, comprising means for generatinga first periodicimpulse wave of a predetermined frequency, means forgenerating a second periodic-impulse wave of said predeterminedfrequency, each of said generating means comprising energy-storagemeans, charging and discharging circuits for said storage means, and avacuum tube included in said charging circuit for effecting periodiccharging and discharging of said storage means, a synchronizing circuitadapted for the reception of a synchronizing-impulse wave of double saidpredetermined frequency and coupled to said generating means forsynchronizing the respective operations, and means for ensuringselective synchronization of said two generating means by successiveimpulses of said synchronizing wave, comprisingan impedance element inseries with the tube in the charging circuit of one of said generatingmeans, and means connecting a control element of the other of saidgenerating means across said impedance element for preventing chargingof the storage means of said other generating means during charging ofthe storage means of said one generating means.

8. A periodic voltage-generating system, comprising means for generatinga iirst periodic wave `of a predetermined frequency, means forgenerating a second periodic wave of said predetermined frequency, eachof said generating means comprising energy-storage means, charging anddischarging circuits for said storage means, and a vacuum tube includedin said charging circuit for effecting periodic charging and dischargingof said storage means, means coupled to said tube for regenerating theaction thereof, and means coupling the charging circuit of one of saidgenerating means to the regenerating means of the other of saidgenerating means for preventing charging of the storage means of saidother generating means during charging of the storage means of said onegenerating means.

9. A periodic voltage-generating system, comprising means for generatinga rst periodic-impulse wave of a predetermined frequency, means forgenerating a second periodic-impulse Wave of said predeterminedfrequency, each of said generating means comprising capacitance means,charging and discharging circuits for said capacitance means, and avacuum tube included in eration thereof by successive synchronizingimpulses, and means coupling the charging circuit of one of saidgenerating means to the regenerating means of the other of saidgenerating means for preventing charging of the capacitance means ofsaid other' generating means during 5 charging oi the capacitance meansof said one generating means.

HAROLD M. LEWIS.

